The CNG hydraulic intensifier is a compact assembly that consists of two gas cylinders separated by a hydraulic cylinder. There is a hydraulic piston that is placed at the center of the piston ride pushes the piston ride assembly back and forth. This drives the gas pistons at each end of the ride. The CNG intensifier uses two stages of compression to provide gas at pressure of as high as 4500 psi and suction pressure of as low as 300 psi. Oil that is pumped into the hydraulic cylinder supplies the power for moving the piston in compressed gas. Due to the action of gas pistons moving back and forth, the gas gets pulled in, compressed and discharged. Then the intake check valve passes gas into the cylinder and the discharge check valve passes gas out of the cylinder. The contamination of the gas is prevented with a set of seals at each end of the hydraulic cylinder. The CNG intensifier doesn’t allow any oil or contaminant into the gas that offers high fuel quality.